This invention relates to surveillance systems. Specifically, the invention relates to a video-based surveillance system that implements a virtual tripwire.
In its original form, a tripwire was an arrangement in which a wire, string, or the like was stretched across a path, and if someone or something happened to trip over the wire or otherwise pull it, some response was triggered. For example, such a response could be detonating a landmine, sounding an alarm, or recording an event (e.g., triggering a counter, camera, etc.). Today, tripwires are often, for example, implemented as beams of light (e.g., laser, infrared, or visible); when someone or something breaks the beam, a response is triggered.
An example of a conventional tripwire using a light beam is shown schematically in FIG. 1. A source generates a beam of light, which is transmitted across a path to a receiver. If the beam is broken, then the receiver no longer receives it. This results in the triggering of some response, as discussed above.
Conventional tripwires are advantageous in that they are at least conceptually simple to use. They also require a minimum of human intervention, once they have been installed.
Conventional tripwires, however, have a number of disadvantages. For example, they can not discriminate between triggering objects of interest and those not of interest. As an example, one may be interested in how many people, but not dogs, walk down a path; however, either a person or a dog would trigger the tripwire. It is also problematic if a group of people walk together, resulting in a single triggering of the tripwire, rather than one for each person.
Furthermore, conventional tripwire arrangements generally involve the installation of dedicated equipment. For example, considering the example of a laser tripwire, a laser source and a laser detector must be installed across a path of interest. Additionally, such dedicated equipment may be difficult to install in such a manner that it is not easily detectable.
Additionally, a conventional tripwire does not afford a high degree of flexibility. Conventional tripwires typically detect if someone or something passes across it, only, without regard to direction of crossing. Furthermore, because they extend in straight lines, only, conventional tripwires are limited as to the regions across which they may be set up.
Conventional video surveillance systems are also in common use today. They are, for example, prevalent in stores, banks, and many other establishments. Video surveillance systems generally involve the use of one or more video cameras, and the video output from the camera or cameras is either recorded for later review or is monitored by a human observer, or both. Such a system is depicted in FIG. 2, where a video camera 1 is trained on the path. Video camera 1 generates video signals, which are transmitted over a communications medium, shown here as a cable 2. Cable 2 feeds one or both of a visual display device 3 and a recording device 4.
In contrast with conventional tripwires, video surveillance systems can differentiate between people and animals (i.e., between objects of interest and objects not of interest) and can differentiate the individuals within a group of people walking together. They further provide flexibility over tripwires, in terms of the shape of the regions they can monitor. Also, because video surveillance systems are so widely used, there is no need to install further equipment. However, video surveillance systems also suffer some drawbacks.
Perhaps the most significant drawback of conventional video surveillance systems is that they require a high degree of human intervention in order to extract information from the video generated. That is, either someone has to be watching the video as it is generated, or someone has to review stored video.
An example of a prior-art video-based surveillance system can be found in U.S. Pat. Nos. 6,097,429 and 6,091,771 to Seeley et al. (collectively referred to below as xe2x80x9cSeeley et al.xe2x80x9d). Seeley et al. is directed to a video security system that includes taking snapshots when an intrusion is detected. Seeley et al. addresses some of the problems relating to false alarms and the need to detect some intrusions/intruders but not others. Image differencing techniques and object recognition techniques are used in this capacity. However, there are many differences between Seeley et al. and the present invention, as described below. Among the most severe shortcomings of Seeley et al. is a lack of disclosure as to how detection and recognition are performed. What is disclosed in these areas is in contrast to what is presented in regard to the present invention.
Another example of a video- and other-sensor-based surveillance system is discussed in U.S. Pat. Nos. 5,696,503 and 5,801,943 to Nasburg (collectively referred to below as xe2x80x9cNasburgxe2x80x9d). Nasburg deals with the tracking of vehicles using multiple sensors, including video sensors. xe2x80x9cFingerprintsxe2x80x9d are developed for vehicles to be tracked and are used to subsequently detect the individual vehicles. While Nasburg does mention the concept of a video trip wire, there is no disclosure as to how such a video tripwire is implemented. Nasburg further differs from the present invention in that it is focused exclusively on detecting and tracking vehicles. In contrast, the present invention, as disclosed and claimed below, is aimed toward detecting arbitrary moving objects, both rigid (like a vehicle) and non-rigid (like a human).
In view of the above, it would be advantageous to have a surveillance system that combines the advantages of tripwires with those of video surveillance systems, and this is a goal of the present invention.
The present invention implements a video tripwire system, in which a virtual tripwire, of arbitrary shape, is placed in digital video using computer-based video processing techniques. The virtual tripwire is then monitored, again using computer-based video processing techniques. As a result of the monitoring, statistics may be compiled, intrusions detected, events recorded, responses triggered, etc. For example, in one embodiment of the invention, the event of a person crossing a virtual tripwire in one direction may trigger the capture of a snapshot of that person, for future identification.
The inventive system may be implemented using existing video equipment in conjunction with computer equipment. It thus has the advantage of not requiring extensive installation of monitoring equipment. The inventive system may be embodied, in part, in the form of a computer-readable medium containing software implementing various steps of a corresponding method, or as a computer system, which may include a computer network, executing such software.
The inventive system may also be used in conjunction with imaging devices other than conventional video, including heat imaging systems or infrared cameras.
One embodiment of the invention comprises a method for implementing a video tripwire system, comprising steps of: installing a sensing device (which may be a video camera or other such device), if one does not already exist; calibrating the sensing device; establishing a boundary as a virtual tripwire; and gathering data.
Further objectives and advantages will become apparent from a consideration of the description, drawings, and examples.
In describing the invention, the following definitions are applicable throughout (including above).
A xe2x80x9ccomputerxe2x80x9d refers to any apparatus that is capable of accepting a structured input, processing the structured input according to prescribed rules, and producing results of the processing as output. Examples of a computer include a computer; a general-purpose computer; a supercomputer; a mainframe; a super mini-computer; a mini-computer; a workstation; a microcomputer; a server; an interactive television; a hybrid combination of a computer and an interactive television; and application-specific hardware to emulate a computer and/or software. A computer can have a single processor or multiple processors, which can operate in parallel and/or not in parallel. A computer also refers to two or more computers connected together via a network for transmitting or receiving information between the computers. An example of such a computer includes a distributed computer system for processing information via computers linked by a network.
A xe2x80x9ccomputer-readable mediumxe2x80x9d refers to any storage device used for storing data accessible by a computer. Examples of a computer-readable medium include a magnetic hard disk; a floppy disk; an optical disk, like a CD-ROM or a DVD; a magnetic tape; a memory chip; and a carrier wave used to carry computer-readable electronic data, such as those used in transmitting and receiving e-mail or in accessing a network.
xe2x80x9cSoftwarexe2x80x9d refers to prescribed rules to operate a computer. Examples of software include software; code segments; instructions; computer programs; and programmed logic.
A xe2x80x9ccomputer systemxe2x80x9d refers to a system having a computer, where the computer comprises a computer-readable medium embodying software to operate the computer.
A xe2x80x9cnetworkxe2x80x9d refers to a number of computers and associated devices that are connected by communication facilities. A network involves permanent connections such as cables or temporary connections such as those made through telephone or other communication links. Examples of a network include an internet, such as the Internet; an intranet; a local area network (LAN); a wide area network (WAN); and a combination of networks, such as an internet and an intranet.
xe2x80x9cVideoxe2x80x9d refers to motion pictures represented in analog and/or digital form. Examples of video include television, movies, image sequences from a camera or other observer, and computer-generated image sequences. These can be obtained from, for example, a live feed, a storage device, an IEEE 1394-based interface, a video digitizer, a computer graphics engine, or a network connection.
xe2x80x9cVideo processingxe2x80x9d refers to any manipulation of video, including, for example, compression and editing.
A xe2x80x9cframexe2x80x9d refers to a particular image or other discrete unit within a video.